In the field of motor vehicle body construction, the interior floor regions of the motor vehicle chassis are typically made from deep-drawn metal floor sheets which are welded together. In the event of a collision-type accident, portions of the colliding vehicle body become deformed, which, in turn, may cause deformation of the welded interior floor sheets. Since the floor sheets are typically sheet metal, there is a high likelihood that, in view of sheet metal's limited pliability, cracks or fractures will develop in the floor region during the collision-induced deformation. This deformation often produces a continuous opening or large fissure in the interior floor which is viewable from the outside. Any opening in the floor is undesirable, since it permits noxious fumes and/or flammable gas or fuel vapors to enter the interior passenger space. This is a particularly serious problem when the fuel tank is located underneath or adjacent to a floor section which is subject to deformation during impact or collision, since in this instance, the fuel tank is also subject to rupture.
In an effort to decrease weight and improve fuel efficiency, modern car bodies are making increasing use of floor sections made of plastics. The use of plastics is desirable since they are readily formable into a variety of surface configurations. In one known configuration (European Patent Application 0 333 267), the floor section of the motor vehicle in the region adjacent the rear trunk and rear seat consists of two substantially horizontal plastic parts which are rigidly interconnected in a box-shaped structure to form a compartment therebetween. This compartment may be utilized for accommodating a spare tire.
In another known configuration for a station wagon, the flooring section in the rear storage region consists of a plastic sheet having a molded recess for a spare tire, along side of which is a second recess for accommodating the fuel tank. It is also a familiar technique to provide a rearwardly disposed reserve seat in a station wagon, wherein the reserve seat faces opposite to the direction of travel. In order to accommodate the feet of a passenger seated on such a rear seat, the rear floor section may be fabricated from a plastic floor sheet having a formed cavity, or step-down recess for the feet. In the alternative, these cavities may also be used to accommodate a spare tire.
In these known examples, the conventional plastics used have little pliancy and are prone to fracture, so that in the event of a major collision, there is still a great danger that deformation of the floor sheet will result in cracking or fracture that would produce an opening in the plastic floor sheet, which, in turn, would expose the interior passenger space to the ambient outside atmosphere. This may result in permitting noxious fumes or flammable gases into the vehicle through the broken and/or torn pieces of plastic, especially if the fuel tank is located under the vehicle chassis in the rear, as is the usual case. Thus, the danger of a fire inside the vehicle is very high for this type of motor vehicle body construction.
German Patent Document DE-OS 32 47 979 discloses a spare tire cavity floor configuration constructed of sheet metal and teaches a method for protecting a fuel tank disposed under the spare tire cavity in the event of a rear end collision. In this design, the front end of the spare tire cavity, as well as a portion of the spare tire, is bridged by an arresting plate, the purpose of which is to transfer lateral force and prop up major deformation of the floor sheet through the rim of the spare tire against a cross-member, such that the fuel tank located beneath the tire cavity is protected against damage resulting from cavity flooring deformation. However, such design does not reduce the danger of fracture to the floor when the spare tire is missing or when a plastic floor and formed cavity is used for holding a spare tire.
In another known example of a motor vehicle interior rear floor construction having a spare tire cavity (German Patent Document DE 34 30 826), the spare tire cavity is made with a variable depth, so that it may accommodate either a narrow width or normal width spare tire. The spare tire cavity is provided with mechanical means for lowering the floor section of the cavity for this purpose. Concertina (accordion-type) walls are provided to the spare tire cavity in order to produce a tight fit connection between the solid floor portion of the spare tire cavity and the surrounding floor section of the trunk. When plastic is used in connection with such a design, there is a great danger of fracture and cracking in and around the cavity region from a rear end collision, and thus flammable gases may still enter into the vehicle.
Even when the fuel tank is not located underneath the rear floor region of a station wagon, a fire danger to the occupants of the station wagon is still present during a rear end collision by another vehicle. In such an event, the front end of the colliding vehicle containing the engine compartment is often deformed and possibly contains fuel, and, as a result of the collision, it is in the immediate vicinity of the rear passenger region of the station wagon. Fuel leaking from the damaged engine compartment of the colliding vehicle may find its way into the station wagon passenger compartment through cracks in the station wagon rear floor regions.
The danger of fire or asphyxiation is still present, even in the situation where these plastic parts are covered with a conventional floor carpeting, since such carpeting is usually only loosely placed within the cavities and not applied in an air-tight manner. Also the fixation of the carpeting to the plastic flooring is such that any moderate degree of stretching induced by a collision will cause the carpet to rip or tear at breakage sites determined by the plastic floor deformation.
Accordingly, there is a clear and urgent need in the art for the design of an improved interior rear floor portion of a motor vehicle of the fracture-prone material type, which includes means for preventing entry of flammable gases and noxious fumes into the interior passenger space of the motor vehicle in the event the plastic floor member becomes deformed from a collision.